1. Technical Field of the Invention
The present invention relates generally to a fuel pressure sensor/sensor mount assembly in which a fuel pressure sensor is so mounted as to exposed to a high-pressure fuel path through which fuel is supplied to a fuel injector, a fuel injection apparatus equipped with a fuel pressure sensor, and a pressure sensing apparatus working to measure the pressure of fuel in a fuel injector.
2. Background Art
In order to ensure the accuracy in controlling output torque of internal combustion engines and the quantity of exhaust emissions therefrom, it is essential to control a fuel injection mode such as the quantity of fuel to be sprayed from a fuel injector or the injection timing at which the fuel injector starts to spray the fuel. For controlling such a fuel injection mode, there have been proposed techniques for monitoring a change in pressure of the fuel upon spraying thereof from the fuel injector.
Specifically, the time when the pressure of the fuel begins to drop due to the spraying thereof from the fuel injector may be used to determine an actual injection timing at which the fuel has been sprayed actually. The amount of drop in pressure of the fuel arising from the spraying thereof may be used to determine the quantity of fuel sprayed actually from the fuel injector. Such actual observation of the fuel injection mode ensures the desired accuracy in controlling the fuel injection mode.
For instance, in the case where a change in pressure of the fuel arising from the spraying of the fuel from the fuel injector (which will also be referred to as a fuel pressure change below) is measured using a fuel pressure sensor installed directly in a common rail (i.e., a fuel accumulator), it will be somewhat absorbed within the common rail, thus resulting in a decrease in accuracy in determining such a pressure change. In order to alleviate this drawback, Japanese Patent First Publication No. 2000-265892 teaches installation of the fuel pressure sensor in a joint between the common rail and a high-pressure pipe through which the fuel is delivered from the common rail to the fuel injector to measure the fuel pressure change before it is absorbed within the common rail.
The fuel pressure change, as produced at a spray hole of the fuel injector through which the fuel has been sprayed, will, however, surely attenuates within the high-pressure pipe. The use of the pressure sensor, as disclosed in the above publication, installed in the joint between the common rail and the high-pressure pipe, therefore, does not ensure the desired accuracy in determining the fuel pressure change. The inventors have studied the installation of the pressure sensor in a portion of the fuel injector which is located downstream of the high-pressure pipe. Such installation, however, has been found to pose the problems, as discussed below.
The inventors have studied a fuel injector in which a branch path is formed which diverges from a fuel inlet path, and a fuel pressure sensor is installed so as to be exposed to the branch path. This structure, however, results in an increase in size of the fuel injector in a direction toward the branch path.
It is, therefore, a first object of the invention to provide a fuel pressure sensor/sensor mount assembly, a fuel injection apparatus, and pressure sensing apparatus which are permitted to be reduced in size without use of the branch path, as described above, and designed to facilitate the ease of installation to an internal combustion engine.
Japanese Patent First Publication No. 2007-231770 discloses a common rail fuel injection system equipped with a fuel pressure sensor which measures the pressure of fuel to be sprayed from a fuel injector. This system has a fuel pressure sensor installed in an end of a common rail to measure the pressure of fuel within the common rail. Japanese Patent First Publication Nos. 2007-270822 and 2007-218249 teach a fuel injector used with the above type of common rail fuel injection system.
Japanese Patent First Publication No. 57-5526 discloses a fuel injector equipped with a built-in fuel pressure sensor which works to measure the pressure of fuel to be sprayed. The fuel injector has a recess formed near a fuel flow path extending through a body of the fuel injector and a strain gauge mounted on the recess to measure a change in pressure of the fuel arising from the spraying of the fuel.
It is, however, impossible for the structures, as disclosed in the above second to fourth publications, to measure the pressure of fuel inputted directly into the fuel injector.
The fuel injector, as disclosed in the above fifth publication, has the recess machined in an outer wall of a lower portion of the body of the fuel injector near the fuel flow path to form the bottom of the recess as a diaphragm which is to be deformed by the pressure of the fuel. The fuel flow path is typically defined by a through hole which is so formed as to extend in a lengthwise direction of the body of the fuel injector. Therefore, in the case where the outer wall of the body of the fuel injector is ground to form the recess, it is difficult to control the thickness of the diaphragm (i.e., the bottom of the recess). This will result in a variation in accuracy of measuring the pressure of fuel among fuel injectors, Particularly, fuel injectors for use in spraying the high-pressure fuel, as disclosed in the above second to fourth publications, are usually made of a high-strength metal in order to ensure the mechanical strength of a body of the fuel injector which is high enough to withstand the pressure of the fuel or designed to have an increased thickness of a wall of the body of the fuel injector near the fuel flow path. The above problems, therefore, become more serious in such a type of fuel injectors.
It is another object of the invention to provide a fuel injection apparatus which is equipped with a fuel pressure sensor and easy to machine without sacrificing the accuracy in measuring the pressure of fuel to be sprayed.
It is a further object of the invention to provide a fuel injection apparatus which is equipped with a fuel pressure sensor and designed to facilitate replacement of the fuel pressure sensor.
In use, the fuel injectors are partially disposed in the engine cylinder, so that mechanical vibrations arising from the combustion of fuel in the engine cylinder are transmitted over the length of a body of the fuel injector. If the diaphragm of the fuel pressure sensor, as discussed above, is oriented perpendicular to the direction in which the vibrations are transmitted (i.e., the length of the body of the fuel injector, the direction in which the diaphragm deforms will coincide with that in which the vibrations are transmitted. This causes the vibrations to be added as an electrical noise to the output of the fuel pressure sensor.
It is, therefore, a still further object of the invention to provide a fuel injection apparatus which is equipped with a fuel pressure sensor and designed to minimize the electrical noise to be added to the output of the fuel pressure sensor.